I presume you've given it a good soaking with GT85 or similar?
The other thing is to use the long bar and scaffold tube to exert a lot of force, while a mate clouts the knuckle of the long bar with a manchester micrometer (hammer
), the shock acting a bit like an impact driver to help release where it's seized.
If you can access a 3/4" drive socket set, you can obviously get a lot more force on that.
I like these kind of challenges. Brute force and igrenance is right up my street
G'luck
Gaz